In many environments, various materials are stored or processed in tanks. These materials include foods, beverages, pharmaceuticals and fuels. Non-contact level sensing gauges are used for such environments. There are several types. Examples include those that use radar transmitters, or ultrasonic waves. A high degree of accuracy has been achieved by the use of level-sensing gauges which monitor content levels by transmitting microwave pulses from an antenna toward the surface of the tank contents. These pulses are reflected from the contents and back to the antenna. Other radar gauges use a frequency modulated continuous wave rather than pulses.
Radar signals are largely unaffected by noise, by air turbulence, or by fluctuations in dielectric constant above a nominal minimum value, density, or conductivity. Even liquids having agitated surfaces or gas bubbles can be reliably measured. Radar sensors are suitable for liquids, solids, powders, granules, dust, corrosive steam and vapors, regardless of the media characteristics, pressures, and temperatures. An example of a radar device 10 mounted on a nozzle flange 11 of a tank 12 is shown in prior art FIGS. 1 and 1A. Inside the device is an antenna 14 at the base of a housing 16 that emits an electromagnetic signal in the form of a microwave 18 which travels through a wave guide 20 and a vapor space 21 toward the surface 22 of a material 24 being measured. When the signal reaches the surface of the material a reflected wave 26 returns in the direction of the antenna. The antenna receives this reflected wave and the electronics 28 in the housing process the information provided by the emitting of waves and the return of waves in a variety of ways, to determine the level of the material in the tank. FIGS. 1 and 1A illustrate one example of a radar device 10. The appearance, materials, and features of the radar system, especially the waveguide 20, vary with the material 24 being measured.
Operators of facilities using tanks need to not only know the levels on a routine basis, but they also need to set safety limits and be alerted during abnormal conditions that bring the level too high. Typically, if a safety limit set at approximately 95% of tank capacity is reached, alarms and other actions result. Facilities having good safety protocols test the system to verify that it will work when needed. Various ways to accomplish this testing have been employed, ranging from electronic measures to raising the level with actual product. Both of these methods have drawbacks. The electronic test which only manipulates the software, does not ensure that the system will function properly since it does not test the measurement device, but rather forces the software to a desired state. Software manipulations are unacceptable to most Safety Integrated Systems checks. Physically moving product is costly and must be closely monitored because if the safety system fails the customer may overfill the tank and cause a recordable incident. Other testing methods involve opening the tank or removing the device. These methods are time-consuming. In many cases the process must be shutdown to safely open the tank or remove the device. This results in lost production and is extremely costly. Therefore there is the need for a device that allows an easy and repeatable method of testing to verify that the safety system will be triggered if the material reaches the safety limit. It is desired that this be “real-world” proof that is easily understood by those implementing the safety checks.